Conventionally, when a steel sheet is worked, a pressing machine is used which is provided with plural pairs of dies having different uses.
For example, JP Pat. No. 3685961 discloses a pressing machine provided with a pair of dies for trimming a drawn steel sheet, a pair of dies for roughly bending the trimmed steel sheet, and a pair of dies for finally bending the roughly bent steel sheet.
The pressing machine can work a plurality of (three) steel sheets existing in different states at the same time.
However, the above-mentioned pressing machine needs an extremely large load for pressing because the plural pairs of dies works the plurality of steel sheets at the same time, which causes a problem of an increase in size of the pressing machine, for example.
JP-A 2000-79424 discloses a technique including drawing a steel sheet with a pressing machine provided with upper and lower dies, trimming the drawn steel sheet with a laser cutter attached to a robot arm, and bending the trimmed steel sheet with a roller attached to the robot arm.
However, adopting the laser cutter needs a high equipment investment because the laser cutter is expensive. Therefore, the technique disclosed in JP-A 2000-79424 has a disadvantage of increase in cost required to trim the steel sheet with the laser cutter.